5,776 research outputs found
Determination of a Definition of Solar Grade Silicon
A definition of solar grade silicon was determined by investigating the singular and the combined effect of the impurities usually found in metallurgical grade silicon on solar cell device performance. The impurity matrix was defined by Jet Propulsion Laboratory Technical Direction Memorandum. The initial work was focussed on standardizing the solar cell process and test procedure, growing baseline crystals, growing crystals contaminated with carbon, iron, nickel, zirconium, aluminum and vanadium, solar blank preparation, and material characterization
Axial form factor of the nucleon in the perturbative chiral quark model
We apply the perturbative chiral quark model (PCQM) at one loop to analyze
the axial form factor of the nucleon. This chiral quark model is based on an
effective Lagrangian, where baryons are described by relativistic valence
quarks and a perturbative cloud of Goldstone bosons as dictated by chiral
symmetry. We apply the formalism to obtain analytical expressions for the axial
form factor of the nucleon, which is given in terms of fundamental parameters
of low-energy pion-nucleon physics (weak pion decay constant, strong
pion-nucleon form factor) and of only one model parameter (radius of the
nucleonic three-quark core).Comment: 23 pages, 5 figures, accepted for publication in J. Phys.
Strong and Electromagnetic Decays of X(1835) as a Baryonium State
With the assumption that the recently observed X(1835) is a baryonium state
we have studied the strong decays of and the electromagnetic decay of in the framework of effective Lagrangian formalism. In the present
investigation we have included the contributions from the iso-singlet light
scalar resonances but we have not included the isospin violating effect. Our
result for the strong decay of is
smaller than the observed data. The decay width for the radiative decay of
is consistent with the assumption that it decays through
the glueball. In addition, the width for the strong decay of is larger than that of the strong decay of due to the large phase space and coupling constant
. From our investigation, it is not possible to interpret
X(1835) as a baryonium.Comment: Corrected typo
Magnetic moment of the pentaquark with light-cone QCD sum rules
In this article, we study the magnetic moment of the pentaquark state as diquark-diquark-antiquark () state in the
framework of the light-cone QCD sum rules approach. The numerical results
indicate the magnetic moment of the pentaquark state is about
.Comment: 10 pages, 1 figure. The main contents of this article is included in
hep-ph/0503007, this article will not be submitted to a journal for
publicatio
Strong CP violation and the neutron electric dipole form factor
We calculate the neutron electric dipole form factor induced by the CP
violating theta-term of QCD, within a perturbative chiral quark model which
includes pion and kaon clouds. On this basis we derive the neutron electric
dipole moment and the electron-neutron Schiff moment. From the existing
experimental upper limits on the neutron electric dipole moment we extract
constraints on the theta-parameter and compare our results with other
approaches.Comment: 18 pages, 2 figures, accepted for publication in Phys. Atom. Nuc
A critical review of the formation of mono- and dicarboxylated metabolic intermediates of alkylphenol polyethoxylates during wastewater treatment and their environmental significance
This is the author's accepted manuscript. The final published article is available from the link below. Copyright @ 2010 Taylor & Francis.Alkylphenoxyacetic acids, the metabolic biodegradation products of alkylphenol ethoxylates, are commonly found in wastewaters and sewage effluents. These persistent hydrophilic derivatives possess intrinsic estrogenic activity, which can mimic natural hormones. Their concentrations increase through the sewage treatment works as a result of biodegradation and biotransformation, and when discharged can disrupt endocrine function in fish. These acidic metabolites represent the dominant alkylphenolic compounds found in wastewater effluent and their presence is cause for concern as, potentially, through further biotransformation and biodegradation, they can act as sources of nonylphenol, which is toxic and estrogenic. The authors aim to assess the mechanisms of formation as well as elimination of alkylphenoxyacetic acids within conventional sewage treatment works with the emphasis on the activated sludge process. In addition, they evaluate the various factors influencing their degradation and formation in laboratory scale and full-scale systems. The environmental implications of these compounds are considered, as is the need for tertiary treatment processes for their removal
Chiral corrections to the vector and axial couplings of quarks and baryons
We calculate chiral corrections to the semileptonic vector and axial quark
coupling constants using a manifestly Lorentz covariant chiral quark approach
up to order O(p4) in the two- and tree-flavor picture. These couplings are then
used in the evaluation of the corresponding couplings which govern the
semileptonic transitions between octet baryon states. In the calculation of
baryon matrix elements we use a general ansatz for the spatial form of the
quark wave function, without referring to a specific realization of
hadronization and confinement of quarks in baryons. Matching the physical
amplitudes calculated within our approach to the model-independent predictions
of baryon chiral perturbation theory (ChPT) allows one to deduce the connection
between our parameters and those of baryon ChPT.Comment: 28 pages, 4 figure
Sigma-term physics in the perturbative chiral quark model
We apply the perturbative chiral quark model (PCQM) at one loop to analyse
meson-baryon sigma-terms. Analytic expressions for these quantities are
obtained in terms of fundamental parameters of low-energy pion-nucleon physics
(weak pion decay constant, axial nucleon coupling, strong pion-nucleon form
factor) and of only one model parameter (radius of the nucleonic three-quark
core). Our result for the piN sigma term of about 45 MeV is in good agreement
with the value deduced by Gasser, Leutwyler and Sainio using
dispersion-relation techniques and exploiting the chiral symmetry constraints.Comment: 19 pages, LaTeX-file, 2 Figure
One-pot Selective Formylation and Claisen Rearrangement on Calix[4]arenes
A versatile synthon with formyl and allyl groups at the upper rim of calix[4]arene has been synthesized in two steps. Selective formylation of 25,27-diallyloxy-26,28-dihydroxycalix[4]arene, along with the Claisen rearrangement of the allyl groups, was achieved by reaction with hexamethylenetetraamine (hexamine) in glacial acetic acid. A control reaction of the dipropyl analogue shows that the selective formylation takes place independently of the Claisen rearrangement. The crystal structure of the dimethylacetal derivative of 5,17-diformyl-11,23-diallylcalix[4]arene is reported
Cluster Control in Oligouranyl Complexes of p-t-Butylcalix[8]arene
Formation of uranyl ion complexes of p-t-butylcalix[8]arene by reaction of the calixarene with [UO2(dmso)5]2+ in the presence of various bases leads to the crystallisation of solids with interestingly different stoichiometry, involving both di- and tri-uranate oligomers bound to the calixarene in anionic species. In all, the calixarene hexa-anion is present in a virtually identical conformation, suggesting that conformational preferences of the ligand must be a major factor controlling the form of the bound oxo-metal complex. Hydrogen bonding to the anions does not appear to be prominent even in the presence of protonated amines and this may explain the formation of some remarkable cation/solvent/simple anion clusters found within the lattices
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